X-ray detectors are known in the art. Many such detectors use a scintillator that reacts to x-rays by producing a corresponding light. A photodiode, in turn, detects this light. Unfortunately, photodiodes often exhibit a strong exponential response to temperature.
The analog detector output is usually amplified and then integrated prior to being converted to a digital form. Such circuitry tends to contribute to an output voltage offset but is itself reasonably stable in at least some regards with respect to temperature. That said, and although the input offset voltage of a corresponding amplifier may be relatively constant, the contribution of this amplifier to an input-referred error current can depend significantly on variations in the photodiode resistance.
Accordingly, when the overall circuit is designed for relatively low input currents, the total direct current gain of the circuit (in particular, the transresistance of the amplifier multiplied by the direct current (DC) integrator gain) is often large. This, in turn, tends to increase the output offset as well as drift. As a general result, then, as temperature increases the zero point can so significantly drift that it can become problematic to reliably distinguish small signal levels. While noise can also present issues in a given application setting, this issue with drift in fact comprises a separate and distinct area of concern.
Elements in the figures are illustrated for simplicity and clarity (though the timing diagrams in a given figure are drawn to a shared temporal axis). Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are sometimes not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.